In LMDS systems (LMDS=Local Multipoint Distribution Service), a field in the grant management sub-header is used to pass status information from the subscriber station to the base station. This status information regards the state of the unsolicited grant service flow.
The unsolicited grant service is designed to support real-time service flows that generate fixed size data packets on periodic bases, such as D1/E1 and voice over IP without silence suppression. The service offers fixed size grants on real-time periodic bases, which eliminates the overhead and latency of subscriber service requests and ensures that grants are variable to meet the flows real time needs.
The most significant bit of the grant management sub-header is the slip indicator bit. The subscriber station shall set this flag once it detects that this service flow has exceeded it's transmit queue depth. Once the subscriber station detects that the service flows transmit queue is back within limits, it shall clear the slip indicator flag.
The flag allows the base station to provide for long term compensation of conditions such as lost maps or clock rate mismatches by issuing additional grants. The base station does not allocate more bandwidth than the maximum sustained traffic rate parameter of the active quality of service parameters, excluding the case when the slip indicator bit of the grant management sub-header is set. In this case, the base station may grant up to 1% additional bandwidth for clock rate mismatch compensation.
It is the object of the present invention to improve constant bit rate services provided in wireless MAN access networks, in particular in LMDS access networks (MAN=Metropolitan Area Network).